1. Field of the Invention
The present invention relates to an automatic focus detection device employed in a microscope.
2. Description of the Related Art
With devices for detecting defects such as cracks, foreign material, and so forth, on a semiconductor wafer or a metal surface, defect detect-ion devices are known having a function of automatic focusing. In Japanese Patent Application Publication No. 2003-7243 disclosed is a focus detection technique in which a laser beam is incident onto a sample so as to capture dark field images of scattered light from the sample, and the sample point is determined to be the focal point at which the dark field image exhibits the greatest brightness.